Just pulled my chevy 383 stroker apart because of a dead cylinder. Found #3 piston missing part of the top ring land. Anybody else had problems? I also found that the exhaust lobe on the camshaft for that cyl was about half flat. I'm thinking that maybe the cam problem may have helped to overheat the piston. The pistons are Keith Black hypereutectic 10.5:1 cr. My machine shop guy said this is a common problem with these pistons, and KB blaims it on tight ring gaps. I trust his knowledge just wanting to see if anyone esle has had the same problem.
They say you have to measure and grind ring end gaps careful! I have them with a three year old build and no problems yet.
Don't know about the pistons being a problem or not, but the flat exhaust lobe can cause contamination of the incoming charge with spent fuel/air, and that can cause detonation, which can cause the piston ring land damage. My personal experience with tight ring gaps has been that it kills the rings and scuffs the cylinders. Not saying that they are wrong though.
Your piston did not cause the flat lobe I would say it was a casualty of the flat lobe. Piston not the problem somthing had to give. My 2 cents
The biggest problem I remember with KB hyper. pistons is you have to gap the top ring bigger or it will **** when the engine is running and lift the top ring land off the piston.... Example-Normally you would gap your rings in the .004 per inch of bore, but with a KB hyper you gap .008 per inch of bore. Its been a long time since I've messed with KB pistons so I dont remember exactly the ring gap for a KB. As for the flat lobe its time for a roller!!
yep. on all counts. the only thing he didn't mention is now is also a good time for forged pistons and a healthy dose of laughing gas.
I found out that I had to run HUGE top ring gaps to make KB pistons live in our claimer engines.. ( alky powered modified ) If we ran .025 to .030 gap ( on a 4.00 bore) it would **** up and shred the piston like confetti !! We ended up running the gap @.050 on the 4.0 bore and .060 on the 4.125 bore... Dave
I agree on the forged pistons, maybe the roller cam, but laughing gas? That would be fun! I was actually thinking about dropping the CP about a point to make it a little more tolerant of today's pump gas.
KB is no more than a cheap piston. Some guys can get by with them racing. I have see many with ring lands broken and I have seen them run 200 NOS on them but the bottom line is there not even close to a good off the shelf piston. I would rather use a TRW off the shelf than the KB's just because I have see many engines with broken KB piston lands that were ***y in good machine shops.I rate the KB's with the old Bager piston used by many cheap rebuilders.. Old TRW pistons are heavy but they will take a lot of abuse and hold up to a lot of heat and NOS. I use a Ross or probe for all decent motors and never had any problems but in comparison price wise there costly.
My machine shop guy recommended Federal-Mogul to replace the KBs. He knows his stuff so that's probably what I'll go with.
Ditto. KB's are great pistons IF YOU READ THE DIRECTIONS. they require a much larger ring gap. try to narrow it up and it will break. But, then again, who ever reads the directions. everything should work perfectly straight from the box. BTW: Aren't nearly all pistons made at the same factory now, then shipped out with different names depending on quality? I know my KB's were forged right next to JE's, SRP', and Ross pistons. Hyper-u pistons are only for slight upgrades.
So the mfg. ring gaps are not right? I have a set of these for my 283 rebuild. I would like to know what I can do to avoid problems. I had a friend that bracket raced a 400 SBC and it went for 2 years without a teardown. That was the main reason I opted for the Hyper U pistons.
Top ring gap must be huge as comapred to normal. Because the heat is contained above the heat dam in those pistons. If the ring gap is normal (or not checked which is common) the ends **** under full throttle and pulls the top off of the pistons. The rings run hottoer so expand much mosre than normal. Don
So, according to their website you need .0065 for every inch of bore. My 283 was 3.875, had to go .060+ 3.935 so at 3.935 x .0065=.0255 or .026" Am I going to be safe with a .026" gap? It's a mild street motor.
Hyper pistons are like gl***. They will tolerate no punishment what so ever !! If you don't believe me put one in the piston press as they shatter into a milloin pieces >>>>.
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